Atomic layer deposition (ALD) is a special type of chemical vapor deposition (CVD) technique. ALD utilizes a sequential exposure of gaseous reactants for the deposition of atomically sized thin films. The reactants are often metal precursors consisting of organometallic liquids or solids used in the chemistry by vaporizing under vacuum and/or heat conditions. The reactants are introduced as a series of sequential, non-overlapping pulses. In each of these pulses, the reactant molecules react with a substrate or wafer surface in a self-limiting way. Consequently, the reaction ceases once all the reactive sites on the wafer/substrate surface are consumed. Between the two pulses, a purge step is applied to remove the excess reactants and byproducts from the process chamber. Using ALD, it is possible to grow materials uniformly and with high precision on arbitrarily complex and large substrates. Some examples of films produced using ALD are SiO2, Si3N4, Ga2O3, GaN, Al2O3, AlN, etc.
The timing diagram of a typical prior art system is shown in FIG. 1. FIG. 1 shows two series of alternating pulses PA and PB of two reactants A and B. The two pulses correspond to time periods TA and TB respectively, which includes a dosing time and any additional wait/purge time required to pump out excess reactant and/or reaction products. This additional wait/purge time for reactants A and B is indicated by wA and wB in FIG. 1. Therefore, the corresponding dosing times for reactants A and B are TA−wA and TB−wB respectively.
The cycle-time of such a prior art system is equal to TA+TB as shown in FIG. 1, consisting of a dose-purge-dose-purge sequence. The cycle is repeated as many times as needed to obtain a film of the desired thickness as required for a given application or recipe. In a plasma enhanced/assisted ALD (PEALD/PAALD) system, a plasma is used for reactant activation in order to trigger the self-limiting reaction on the heated substrate. In contrast, in a thermal ALD system, high temperature is used for facilitating the reaction.
There are many different techniques for performing ALD in the prior art. U.S. Pat. No. 7,314,835 to Ishizaka, discloses a method for depositing a film on a substrate using a plasma enhanced atomic layer deposition (PEALD) process. The method includes disposing the substrate in a process chamber configured to facilitate the PEALD process. A first process material is introduced within the process chamber, and a second process material is introduced within the process. Radio Frequency (RF) power of more than 600 Watts (W) is coupled to the process chamber during the introduction of the second process material. This results in the generation of a plasma that accelerates a reduction reaction between the first and second process materials at a surface of the substrate. The film is formed on the substrate by alternatingly introducing the first process material and the second process material.
U.S. Pat. No. 7,341,959 to Brcka also discloses a method for depositing a film on a substrate using a plasma enhanced atomic layer deposition (PEALD) process. The method includes disposing the substrate in a process chamber configured to facilitate the PEALD process. The process chamber includes a substrate zone proximate to the substrate and a peripheral zone proximate to a peripheral edge of the substrate. The method also includes introducing a first process material and a second process material within the process chamber and coupling RF power to the process chamber during the introduction of the second process material. This results in the generation of a plasma that facilitates a reduction reaction between the first and the second process materials at a surface of the substrate.
Furthermore, RF power is coupled to a process electrode to generate a substrate zone plasma in the substrate zone that ionizes contaminants substantially in a region of the substrate. RF power to a peripheral electrode generates a peripheral zone plasma in the peripheral zone having a characteristic different from the substrate zone plasma. As a result, the ionized contaminants are transported from the substrate zone to the peripheral zone in the process chamber.
U.S. Patent Publication No. 2017/0016114 A1 to Becker discloses a gas deposition chamber. The chamber includes a volume expanding top portion and a substantially constant volume cylindrical middle portion and optionally a volume reducing lower portion. An aerodynamically shaped substrate support chuck is disposed inside the gas deposition chamber with a substrate support surface positioned in the cylindrical middle portion. The top portion reduces gas flow velocity. The aerodynamic shape of the substrate support chuck reduces drag and promotes laminar flow over the substrate support surface. The lower portion increases gas flow velocity after the substrate support surface. The gas deposition chamber is configurable to 200 millimeter diameter semiconductor wafers using ALD and or PEALD cooling cycles. A coating method includes expanding process gases inside the deposition chamber prior to the process gas reaching a substrate surface. The method further includes compressing the process gases inside the deposition chamber after the process gas has flowed passed the substrate being coated.
U.S. Patent Publication No. 2012/0141676 A1 to Sershen teaches an ALD coating system. The system includes a fixed gas manifold disposed over a moving substrate with a coating surface of the substrate facing precursor orifice plate. A gas control system delivers gas or vapor precursors and inert gas into the fixed gas manifold which directs input gases onto a coating surface of the moving substrate. The gas control system includes a blower interfaced with the gas manifold which draws gas through the gas manifold to remove unused precursors. Also removed are inert gas and any reaction byproduct from the coating surface. The gas manifold is configured to segregate precursor gases at the coating surface to prevent the mixing of dissimilar precursors. The gas manifold may also segregate unused precursor gases in the exhaust system so that the unused precursors can be recovered and reused.
U.S. Pat. No. 8,940,646 to Chandrasekharan discloses methods of depositing layers of material on multiple semiconductor substrates at multiple processing stations within one or more reaction chambers. The methods include dosing a first substrate with film precursor at a first processing station and dosing a second substrate with film precursor at a second processing station. This is done with precursor flowing from a common source such that the timing of the dosing is staggered. In other words, the first substrate is dosed during a first dosing phase during which the second substrate is not substantially dosed, and the second substrate is dosed during a second dosing phase during which the first substrate is not substantially dosed. Also disclosed are apparatuses having multiple processing stations contained within one or more reaction chambers. Further disclosed is a controller with machine readable instructions for staggering the dosing of first and second substrates at first and second processing stations.
U.S. Pat. No. 9,343,296 to LaVoie discloses methods of forming SiC/SiCN film layers on surfaces of semiconductor substrates. The methods include introducing a silicon-containing film-precursor and an organometallic ligand transfer reagent into a processing chamber. This results in adsorbing the silicon-containing film-precursor, the organometallic ligand transfer reagent, or both onto a surface of a semiconductor substrate such that either or both form an adsorption-limited layer. The methods also include reacting the silicon-containing film-precursor with the organometallic ligand transfer reagent, after either or both have formed the adsorption-limited layer. The reaction results in the forming of the film layer. In other variations, a byproduct is also formed which contains substantially all of the metal of the organometallic ligand transfer reagent. The methods include removal of the byproduct from the processing chamber. Also disclosed are corresponding semiconductor processing apparatuses for forming SiC/SiCN film layers.
U.S. Patent Publication No. 2011/0003087 A1 to Soininen discloses a reaction chamber of a reactor for coating or treating a substrate by an ALD process. This is accomplished by exposing the substrate to alternately repeated surface reactions of two or more gas-phase reactants. The reaction chamber is configured to generate capacitively coupled plasma and comprises a reaction space within the reaction chamber. It also comprises a first inlet to guide gases into the chamber and an outlet to lead gases out of the chamber. The reaction chamber is configured to lead the two or more reactants into the reaction chamber. This is done such that the two or more reactants may flow through the reaction space across the substrate in a direction essentially parallel to the inner surface of the lower wall.
Non-Patent Literature (NPL) reference of “Plasma-Assisted Atomic Layer Deposition Al2O3 at Room Temperature” by Tommi O. Kaariainen dated 2009 teaches a design of plasma source used for PEALD of Al2O3 films at room temperature. In their reactor, the plasma is generated by capacitive coupling and directly in the deposition chamber adjacent to the substrate. However, it can be separated from it by a grid to reduce the ion bombardment while maintaining the flow of radicals directly to the substrate surface.
During the ALD cycle, a mixture of nitrogen and argon is introduced into the reactor to act as a purge gas between precursor pulses and to facilitate the generation of a plasma during the plasma cycle. Sequential exposures of TriMethylAluminum (TMA) and excited O2 precursors are used to deposit Al2O3 films on Si(100) substrates. A plasma discharge is activated during the oxygen gas pulse to form radicals in the reactor space. The experiments show that the growth rate of the film increased with increasing plasma power and with increasing O2 pulse length before saturating at higher power and longer O2 pulse length. Their growth rate saturated at the level of 1.78 Angstrom (A) per cycle.
U.S. Pat. No. 4,282,67 to Kuyel teaches a method and system for generating plasma using an RF-excited radial-flow, cylindrical plasma rector. The reactor includes a toroidal waveguide of rectangular cross-section connected to a microwave source. One of the reactive species of the plasma is flowed through the waveguide and is pre-ionized. The design permits independent control over the activation of both reactive species.
It is believed that widespread adoption of ALD technology for a variety of promising industrial applications is predicated upon obtaining a film thickness that is extremely uniform across the substrate and has very little or no hydrogen content. It is also important to reduce the cycle-time for the production of the film so that operational throughput can be increased. Such an increased throughput would result in reduced costs and other economies of scale. Furthermore, in traditional ALD systems, Ammonia (NH3) is used for nitridation. NH3, being a corrosive chemical, incurs a high downstream cost of abatement as known by those skilled in the art.
The prior art cited above fails to accomplish these goals. More specifically, the prior art is ineffective at producing extremely uniform films across the substrate surface with short cycle-times. That is because the high energy plasma flux is able to enter from the plasma chamber of typical prior art designs into the ALD volume around the substrate. Such prior art designs may use a showerhead (Chandrasekharan, LaVoie, Soininen) or a grid (Kaariainen) to separate the plasma from the substrate. The plasma is also sometimes pulsed to minimize exposure to the substrate or to reduce the energy of the plasma ions/flux.
In any case, the result is that high energy plasma flux still manages to enter the ALD volume and gets into contact with the substrate. This results in the damaging of the substrate surface and deterioration of the deposited film quality. Furthermore, the cycle-times in typical designs cannot be significantly reduced. As a result, the prior art is unable to satisfy the very high quality and uniformity, low cost and high throughput requirements of many industrial applications.